Inventory and POS/Cash Solutions

I'm looking into buying a Convenience Store. One thing I want to do is have it's inventory and POS/Cash systems upgraded. So I want to know the best linux solution to handle that (while avoiding SAP and Oracle bloat). I found a list of Linux ERP solutions below. But I want to know how I can go about evaluating them.
- http://www.linuxlinks.com/article/20091129070817552/ERP.html

Also, I want to know how to find a consultant / technician that has setup inventory control and other systems for convenience or retail stores. The immediate task(s) would be things like:
- setup inventory control hardware & software
- all product ( inventory and sales ) must be trackable by barcode
- software should track
- prod w/ highest sales volume
- prod w/ best margin
- reorder threshold
- tie sales numbers to employee shifts